The distinct metamorphic stages and structural styles of the 1.94–1.86 Ga Snowbird Orogen, Northwest Territories, Canada

• Published in: Journal of Metamorphic Geology
• Main Authors: Thiessen, Eric J., Gibson, H. Dan, Regis, Daniele, Pehrsson, Sally J., Ashley, Kyle T., Smit, Matthijs A.
• Other Authors: Natural Sciences and Engineering Research Council of Canada
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Geochemistry and Petrology; Geology; Northwest Territories
• Online Access: http://dx.doi.org/10.1111/jmg.12556; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjmg.12556; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jmg.12556; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jmg.12556

Abstract Palaeoproterozoic orogenesis within the Archean southeastern Rae craton is related to the initial amalgamation of Laurentia. Characterizing the accompanying tectonic processes during this time has been complicated due to polymetamorphism, which results in the obscuring of the age record of the terranes involved. To improve the knowledge of the tectonic evolution of the South Rae Craton, petrologic and structural analyses are applied in conjunction with in situ trace element chemistry, inclusion barometry, U–Pb monazite and titanite, and Lu–Hf garnet chronology. The data robustly constrain Palaeoproterozoic pressure–temperature–time paths of major deformational events along the southeastern Rae craton margin. D 1 occurred between 1.94 and 1.93 Ga in the Dodge‐Snowbird domain, which included prograde burial of metasedimentary rocks, deposited at 2.2–2.0 Ga, and the development of migmatitic layering and east‐southeast trending folds (S 1 , F 1 ). Peak metamorphism is recorded in metasedimentary units at c . 1.93 Ga when rocks reached conditions of 9.0–10.5 kbar and 810–830°C. Within the Dodge‐Snowbird domain, D 2 imparted north‐northeast trending open folds and associated axial planar cleavage (S 2 , F 2 ) between 1.93 and 1.90 Ga during east‐west compression that appears to have been synchronous with cooling and exhumation. Later D 2 deformation, localized within the Wholdaia Lake shear zone (WLsz; S T1 ), developed in the footwall of this thrust‐sense structure at 1,873 ± 5 Ma at conditions of 9.5–11.0 kbar and 820–850°C. The hangingwall Dodge‐Snowbird domain had already cooled to below 300°C by then, indicating a significant structural and metamorphic break across the domain's western boundary. A new phase of unroofing (D 3 ) involved pervasive amphibolite‐ to greenschist facies extensional shearing (S T2 ) within the WLsz, which overprinted S T1 foliations between 1.87 and 1.86 Ga. Continued greenschist facies shearing younger than 1.86 Ga likely ended by c . 1.83 Ga when lamprophyre dykes cut the ...